destroying an altar is a task for melee users like fighter/warrior or ranger/assassin or defender/guardian.
As an archer, you should function as a "back-up" person, which is helping your own party from a distance. I knew that there wouldn't need to try to destroy an altar. It has a high magic resistance and shooting defense, or it would be very easy to get it
the altar in canta is not same as 1-15 though.